Heat storage for room and tap water heating

ABSTRACT

Heat storage for house warming over half a year can be constructed from the following principles: A large water volume typically around 10 000 m 3  is necessary to keep the ratio of the heat loss through the surface compared to the heat content in the volume low. To assist the heat loss prevention the storage is isolated on the sides and on the top. From the non-isolated bottom and upwards a cooler zone is developed over half a year because of heat conduction to the ground. The approximate thickness of the temperature transition zone can be estimated to 2.5 m

The aim of the invention is to store warm water for warming houses and other common household applications during wintertime.

According to the construction principles described below the warm water storage will with the present technology be sufficient warm water storage for indoor heating and other warm water applications in the household for about 25 separate one family houses in the temperate zones for half a year provided the warm water storage is filled with water at a temperature around 60 degrees centigrade. The time for the practical use is referred to as the application time.

A typical construction will be a box shaped basin with a cross sectional area of 30 m×30 m and a depth of 10 m, filled with water. The storage is isolated on the top and on the sides to such a degree that the heat loss through the isolated part is 0.05 W/m²K or lower. Only the bottom is not isolated. From the bottom and upwards a cooler zone of around 2.5 m will be forming during a half year period. The useful part of the storage are the water layer above this zone.

The 2.5 m referred above are based on a mathematical proof for the development of a transient cooling phenomenon in still water from the cooler bottom and upwards into the heated regions progressing over half a year. The calculation gives that the major part of the temperature drop lies within this zone (ref.: VARME, 44. aargang 1979, Dec. nr. 6, p. 127, Christen F Pedersen. Tekn. Inst. Gregersensvej, DK 2630 Taastrup)

A Heat storage for room and tap water heating with an application time equal to half a year is designed by using the following prescriptions, which must all be fulfilled. 

1. The storage is ideally being shaped as a basin with a plane horizontal bottom and vertical sides filled with water
 2. The top and sides are isolated with Polystyrene or any other material until a heat loss below 0.05 W/m²K is obtained on the isolated parts. The bottom is not isolated.
 3. The ratio of the water volume to the area of the isolated part of the surface of the water is at least 4 m. All geometrical quantities in the above are assumed to be within common craftsman-like accuracy. 